1. Field of the Invention
The present invention relates to a variable valve timing control apparatus for an internal combustion engine.
2. Description of Related Art
JP-A-9-324613 (U.S. Pat. No. 5,738,056) or JP-A-2001-159330 (U.S. Pat. No. 6,330,870) describes an oil-pressure drive type variable valve timing device for an engine, in which a rotation phase of a camshaft with respect to a crankshaft is locked into a middle lock phase when the engine is stopped. The rotation phase of the camshaft with respect to the crankshaft is defined as variable cam timing (VCT) phase. The middle lock phase is located approximately middle in a controllable range of the VCT phase. A controllable range of the valve timing is enlarged by setting the middle lock phase.
The middle lock phase is set suitably for start-up of the engine. The engine is activated in a state where the VCT phase is locked into the middle lock phase. When the start-up of the engine is completed, an oil pressure is raised to an appropriate value by speed-up of the engine (increase in rotation of oil pump). Then, oil is filled into the timing device, and the VCT phase is unlocked and controlled into a target VCT phase in accordance with an operation state of the engine.
Because the VCT phase is locked at the middle lock phase while the engine is stopped, after the engine is restarted, it is necessary to quickly fill oil into both of an advance chamber and a retard chamber. A communication passage is defined to connect the advance chamber to the retard chamber while the VCT phase is locked, and oil supplied to the advance chamber is further supplied to the retard chamber through the communication passage. Further, an oil supply passage of the retard chamber is connected to a drain passage, and air in the retard chamber is discharged into the drain passage. Thus, oil can be easily and accurately filled into the chambers.
However, a part of oil filled into the retard chamber may be directly discharged into the drain passage. In this case, oil is consumed in vain, and lubricating oil may be shorted for the engine while oil is filled into the chambers, so that lubricating property of the engine may become worse.